High temperature grease compositions

ABSTRACT

GREASE COMPOSITION COMPRISING A MINERAL LUBRICATING OIL THICKENED TO GREASE CONSISTENCY HAVING INCORPORATED THEREIN MINOR AMOUNTS EACH OF A PHEOTHIAZINE-TYPE INHIBITOR AND A POLYESTER OF A C1-20 ALCOHOL AND A C3-20 CARBOXYLIC ACID, HAVE IMPROVED HIGH SPEED, HIGH TEMPERATURE LUBRICATING PROPERTIES.

United States Patent HIGH TEMPERATURE GREASE COMPOSITIONS Joshua D. Smith, New Orleans, and Marion A. Clifton, Holson, La., assignors to Shell Oil Company, New

York, N.Y. No Drawing. Filed June 23, 1969, Ser. No. 835,725 Int. Cl. ClOm 5/22 US. Cl. 252-28 9 Claims ABSTRACT OF THE DISCLOSURE Grease compositions comprising a mineral lubricating oil thickened to grease consistency having incorporated therein minor amounts each of a phenothiazine-type inhibitor and a polyester of a C alcohol and a C carboxylic acid, have improved high speed, high temperature lubricating properties.

This invention relates to grease compositions having improved high speed, high temperature lubricating properties. More particularly, the invention relates to grease compositions comprising an oleaginous lubricant base thickened to grease consistency having incorporated therein a combination of a phenothiazine-type inhibitor and a polyester formed by reacting monoor polyfunctional alcohols and acids as hereinafter described.

Greases possessing good high speed lubricating characteristics are required in a variety of industrial applications, particularly in the lubrication of bearings, such as, for example, electric motor bearings. Products of this type must be capable of lubricating wearing surfaces for extended periods of time at temperatures of as high as 300 F. and above, and must therefore possess good high temperature bearing life and oxidation stability properties. In this latter respect a class of very effective oxidation inhibitors are those of the phenothiazine type, e.g., phenothiazine and various phenothiazine derivatives such as N- substituted and dialkyl substituted phenothiazines. Although these compounds are known to be highly efficacious antioxidants, they have found only limited application'in mineral lubricating oil based greases because of their tendency to form large macroscopic crystals in these products which renders the, greases unsuitable formany lubricating applications. These crystals generally form in I the finished grease during storage or after use at a high temperature. it has been-theorized that the phenothiazine compounds, which are normally added as minute crystals, dissolve or melt in the grease when exposed to avhigh temperature environment. Upon subsequent cooling it is thought that the inhibitor rapidly recrystallizes with the formation of large macroscopic crystals, e. g., 300 microns and larger. These very large crystals not only destroy the homogeneity of the product and detract from its appearance, but also are readily removed if the product is pumped through a screen or other filter device, e.g., a 100 mesh wire screen having 149 micron openings. This of course deleteriously affects the oxidation stability of the product and can result in bearing failures.

It has now been found that grease compositions comprising an oleaginous lubricant base thickened to grease consistency and having incorporated therein (1) from 0.1% to 3.0% by weight of a phenothiazine-type inhibitor and (2) from 7% to 30% of a polyester of a C alcohol and a C carboxylic acid, not only aiiord a means of overcoming the inhibitor recrystallization problem of the prior art, but additionally and unexpectedly possess exceptionally long bearing lives, and perform exceedingly well over a wide range of temperatures.

iice

It is noteworthy that the unique properties displayed by the compositions of the invention in substantially eliminating the inhibitor recrystallization problem, were not exhibited by many other combinations tested and found to be unacceptable. Among the potential recrystallization retarders investigated and found unsuitable were: 4-amino methyl piperidine, diethyl ethylene glycol monoethyl ether, pyridine, 2-amino-l-butanol, polyoxylene sorbitan monooleate, 2-methyl-5-ethyl pyridine, butyl stearate, cresyl diglycol carbonate, diethyl hydroxylamine, dipropylamine, morpholine, propylene carbonate, tributylamine, phenyl cyclohexylamine, polyethylene glycol polymer, N-coco morpholine, butyl benzoate, diethyl carbonate, toluene, dipropylene glycol, dibutylamine, dialkyl thiourea, N- phenyl cyclohexylamine, dibutylamine, Polyamine H (polyethylene polyarnine), tributyl phosphate and diethylene glycol monobutyl ether.

In view of the large number of compounds including many well known solvents and simple esters which did not satisfactorily prevent inhibitor recrystallization, it is surprising that the polyesters of the invention would be so highly effective in retarding crystal growth, and even more surprising that the combination of the esters with the phenothiazine compound in the amounts specified would markedly improve the bearing lives of mineral oil based greases.

Phenothiazine-type inhibitors which can be employed in the present compositions include unsubstituted phenothiazine, N-substituted phenothiazines and alkyl-substituted phenothiazines. The N-substituted phenothiazines preferably have one alkyl or al-koxy radical substituent on each aromatic ring of the phenothiazine molecule. The alkyl or alkoxy substituents can have from 1 to 12 carbon atoms and are preferably substituted in the 3,7 positions. The N substituent can be an alkyl, aryl, alkaryl, aralkyl or a cyanoalkyl radical having from 1 to 12 carbonatoms. Examples of suitable alkyl-substituted phenothiazines include 3,7-dibutyl phenothiazine, 3,7-dioctyl phenothiazine and the like. N-substit-uted phenothiazines, which are useful for the purposes of the present invention include N-methyl-3,7-dioctyl phenothiazine, N-n. butyl- 3,7-dioctyl phenothiazine, N-n. octyl-3,7-dioctyl phenothiazine, 'N-cyanoethyl-3,7-dioctyl phenothiazine, N-cyanobutyl-3,7-dioctyl phenothiazine, N-benzyl-3,7-dioctyl phenothiazine, N-benzyl-3,7-dibutyl phenothiazine, N-benzyl-3,7-diisopropoxy phenothiazine, N-benzyl-3,7-dibutoxy phenothiazine and mixtures thereof. Unsubstituted phenothe invention. These compounds and their methods of thiazine and N-benzyl-3,7-dioctyl phenothiazine have been found to be particularly advantageous for the purposes of preparation are known to the art.

The polyesters contemplated for use in the present compositions can be formed from alcohols having 1 to 20, especially from 4 to 12 carbon atoms, and carboxylic acids having from 3 to 20, especially from 4 to 12 carbon atoms. By the term polyester is meant the reaction product of a polyfunctional acid with one or more alcohols, or of apolyfunctional alcohol with one or more acids. The term polyester as herein defined encompasses both complex esters and non-complex esters and various mixtures thereof.

Alcohols which can be used to prepare the polyesters include monohydric alcohols such as'methyl, butyl, isooctyl and dodecyl alcohols; dihydric alcohols such as 2-ethyl-l,3hexanediol, 2-propy1-3,3-heptanediol, 2-butyl- 1,3-butanediol, 2,4-dimesityl-1,3-butanediol and propylene glycols in the specified carbon number range. Polyhydric alcohols having 3, 4, 5 or more hydroxyl groups per molecule are very suitable, particularly such polyols as pentaerythritol, dipentaerythritol and trimethylolpropane.

Carboxylic acids suitable for making the polyester constituent include monoand dibasic carboxylic acids such as butyric, valeric, sebacic, azelaic, suberic, succinic, caproic, adipic, ethyl suberic, diethyl adipic, thapsic, malonic, glutaric, diglycolic, pentadecanedicarboxylic, thiodiglycolic, pelargonic, propionic, caprylic, decanoic, lauric, palmitic, pimelic, phthalic and the like.

Examples of suitable polyesters include di(2-ethylhexyl) sebacate, di-(Z-ethylhexyl) azelate, ethyl glycol dilaurate, di-(1,3-methylbutyl) adipate, di-(l-ethylpropyl) azelate, diisopropyl oxylate, dicyclohexyl sebacate, diisooctyl phthalate, diisodecyl phthalate, glycerol tri-n-heptoate, di- (undecyl) azelate, and tetraethylene glycol di-(Z-ethylene caproate), and mixtures thereof.

Especially advantageous polyesters are the fatty acid esters of pentaerythritol, dipentaerythritol and trimethylolpropane and mixtures thereof. Examples of these esters are pentaerythrityl tetrabutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentaerythrityl dibutyratedicaproate, pentaerythrityl butyrate caproate divalerate, pentaerythrityl butyrate trivalerate, pentaerythrityl butyrate tricaproate, pentaerythrityl tributyratecaproate, mixed C saturated fatty acid esters of pentaerythritol, dipentaerythrityl hexavalerate, dipentaerythrityl hexavalerate, dipentaerythrityl hexacaproate, dipentaerythrityl hexaheptoate, dipentaerythrityl hexacaprylate, dipentaerythrityl tributyratecaproate, dipentaerythrityl trivalerate tricaproate, dipentaerythrityl mixed hexaesters of C fatty acids and trimethylolpropane heptanoate. Pentaerythrityl esters of mixtures of C acids have been found to be particularly effective in the present compositions. This product is commercially available from Hercules, Inc., under the trade name Hercolube A.

The oleaginous lubricant base into which the phenothiazine-type inhibitors, and synthetic esters are incorporated are hydrocarbon lubricating oils, preferably mineral lubricating oils which include those derived from naphthenic base, paraffinic base, or mixed base crudes having a viscosity in the range of from 50 SSU at 100 F. to about 300 SSU at 210 F. Also included in this range are hydrotreated bright stocks having molecular weights of 500 to 2000 or higher. Other suitable base stocks include synthetic hydrocarbons such as polyolefins, synthetic oils such as polyalkylene glycols, and mixtures of synthetic hydrocarbons and mineral lubricating oils.

The oleaginous lubricant base can be thickened with a wide variety of thickeners such as soap-base thickening per 100 grams. Bentonites, in particular magnesium bentonites, sometimes referred to as hectorites, are preferred. These clays are normally made oleophilic by adsorption of, or reaction with, organic ammonia bases or their salts.

The phenothiazine-type inhibitors can be incorporated in the compositions of the invention in concentrations of 0.1% to 3% by total composition weight. Experience has shown that inhibitor concentrations of 0.4% to 2% by weight is normally sufficient to achieve the desired effects. The polyester can be employed in the present compositions in amounts of from 7% to 30% by total composition weight, but preferably in concentrations of 10% to 25% by weight.

In addition to the phenothiazine-type inhibitor and polyesters, other additives can also be incorporated into the invention grease compositions, for example, anti-corrosion agents such as sodium nitrite, sodium sebacate, aminoor benzo-triazoles, glycerol monooleate, etc.; additional antioxidants such as phenyl-beta-naphthylamine, metal dithiocarbamates, dilauryl selenide, etc.; viscosity index improvers such as methacrylate polymers and copolymers; extreme pressure agents, and any other additive recognized in the art to perform a particular function or functions.

The grease compositions of the invention can be prepared by methods well known to the art and their effectiveness generally is not dependent on their method of preparation or on the order of adding the various constituents. Normally, the thickening agent is incorporated into the oleaginous lubricant base first and then the phenothiazine inhibitor and synthetic ester are added either separately or as a mixture.

EXAMPLE I In order to demonstrate the surprising effectiveness of the compositions of the invention in respect to high speed bearing performance, a series of grease compositions were prepared and subjected to the Navy High Speed Bearing Test which is described in Federal Test Method 331.1. In this test, a ball hearing was operated at 10,000 r.p.m. at a temperature of 300 F. as outlined in the test procedure. The bearing life for each of the compositions shown in Table I represents the length of time the test was conducted before a bearing failure occurred. All of the compositions tested were mineral oil based greases which had been thickened with either clay or soap-base gelling agents. The results of the bearing performance tests are recorded in the following table.

B. Water-prooied montmorillonite clay.- Oxidation inhibitor:

0. Phenothiazine;

D. N-benzy1-3,7-dloctyl phenothiazine;

Synthetic fluid:

E. Hercolube A (pentaerythrityl ester of mixtures of 04-: fatty acids);

F. Diisocctyl phthalat G. Hercolube F (dipentacrythrityl ester of mixtures of 05-10 fatty acids). H. Ucon LB 170 X (polyoxyalkylenc glycol).

agents, organic thickeners or clay thickeners. Suitable soap-based thickeners include any metal soap of a fatty acid which is capable of providing a stable gel structure to oleaginous base fluids. The term soap-base is intended to cover conventional metal soaps, complex soaps and mixed base soaps. Especially advantageous soap-base thickeners are the lithium soaps, in particular lithium hydroxy stearate.

Suitable clay thickeners should have a substantial base The results shown in Table I indicate the grease compositions containing a phenothiazine type-inhibitor alone (Composition 1), or a phenothiazine inhibitor with a polyester fluid not in accordance with the invention (Composition 2), have relatively short bearing lives. In contrast, Compositions 3, 4 and 5 containing the inhibitorpolyester combination of the invention have bearing lives of up to 3445 hours. Comparison test results obtained exchange capacity, normally at least 25 milliequivalents on two commercial lithium soap thickened greases further illustrate the remarkable advantages displayed by the compositions of the present invention.

EXAMPLE II To further demonstrate the outstanding properties of the present greases, Composition 3, a lithium soap based grease, was subjected to the ABEC Bearing Rig test as set out in Federal Test Method Std. No. 791(a), Dec. 31, 1961, Method 333, Par. 2.2(b). This test was conducted on an ABEC testing machine which was operated at 10,000 r.p.m. and a temperature of 350 The test apparatus was developed by the Bearing Engineers Committee of the Anti-Friction Bearing Manufacturers Assoc. and is described in their Technical Bulletin No. 5. Under the very severe conditions of this test, Composition 3 performed satisfactorily for 745 hours. This result was quite surprising since lithium soap thickened greases generally have dropping points in the range of 380 F. and consequently would be expected to liquefy and run out of hearings in a relatively short time at this elevated temperature.

EXAMPLE III In addition to increasing high temperature bearing performance, the compositions of the invention have been found to be substantially free of macroscopic size crystals which frequently occur when phenothiazine-type inhibitors are employed in mineral oil based greases. To further demonstrate the beneficial effects obtained by practice of the present invention, a series of compositions were prepared and microscopically examined at periodic intervals to determine the extent and character of the crystal formation within the grease. The results of these observations are shown in Table H. The letter designations representing the synthetic fluids and thickeners em- The effectiveness of the present compositions in retarding inhibitor recrystallization is clearly evident from the foregoing data. The size of the inhibitor crystals is extremely critical in lubricant systems wherein the grease is filtered through a fine mesh screen to remove sus- 5 pended particulate matter WhlCh might 1111111'8 bearing surfaces. Frequently employed screens of this type have openings of 149 microns or less mesh screen U.S. Sieve standard size) and would obviously remove a substantial amount of the inhibitor present in Compositions 6 and 8, while filtering the compositions of the invention would not reduce the inhibitor concentration.

We claim as our invention:

1. A grease composition consisting essentially of a major amount of mineral lubricating oil thickened to grease consistency having incorporated therein (1) from 0.1% to 3.0% by weight of a phenothiazine inhibitor and (2) from 7 to 30% of a polyester of a C alcohol and C carboxylic acid.

2. The composition of claim 1 wherein the phenothiazine-type inhibitor is present in the amount of from 0.4% to 2.0% by weight and the polyester is present in amounts of from 10% to 25% by weight.

3. The composition of claim 1 wherein the inhibitor is selected from the group consisting of phenothiazine, N-'C hydrocarbyl substituted phenothiazine and C dialkyl substituted phenothiazine.

4. The composition of claim 1 wherein the alcohol has 4 to 12 carbon atoms and the carboxylic acid has 4 to 12 carbon atoms.

5. The composition of claim 3 wherein the alcohol is selected from the group consisting of pentaerythritol, dipentaerythritol, trimethylolpropane and mixtures thereof and the carboxylic acid is an aliphatic monocarboxylic acid having 4 to 12 carbon atoms.

6. The composition of claim 2 wherein the inhibitor is phenothiazine.

7. The composition of claim 6 wherein the polyester is a pentaerythrityl ester of mixtures of C fatty acids.

8. The composition of claim 7 wherein the lubricating oil is thickened to grease consistency by use of a lithium soap. 7

9. The composition of claim 7 wherein the lubricating oil is thickened to grease consistency by the use of a water-proofed montmorillonite caly.

References Cited UNITED STATES PATENTS 2,781,318 2/1957 Cyphers 252-47 2,801,219 7/1957 Buckmann 252--28 3,083,163 3/1963 Perms 252-28 3,134,736 5/1964 Sarraf et al 252-28 3,218,256 11/1965 Edwards et a1 252--47 3,349,034 10/ 1967 Butcosk et a1 252-28 3,370,007 2/ 1968 Caruso 252-28 3,461,068 8/1969 Peacock 25228 DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner U.S. Cl. X.R. 25242.1. 47, 47.5 

